introduction to modeling
DESCRIPTION
Introduction to Modeling. Define the terms System Surroundings Input/output Transducer Distinguish between sensors and actuators For a given transducer, identify the appropriate inputs and outputs For a given transducer, find find/calculate span , full scale output , s ensitivity , - PowerPoint PPT PresentationTRANSCRIPT
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Introduction to Modeling
Define the terms System Surroundings Input/output Transducer
Distinguish between sensors and actuators For a given transducer, identify the
appropriate inputs and outputs For a given transducer, find find/calculate
span, full scale output, sensitivity, accuracy, and resolution
Distinguish between static and dynamic response characteristics of transducers
For a given transducer, find find/calculate
response time, overshoot, gain, and phaseshift, and
Explain the concept of resonance
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Some definitions
System:Region of space set aside for analysis
Boundary:Defines a system such that everything within it is the system
Surroundings:Everything outside the system
Interactions between the system and surroundings:• Inputs from surroundings to the system• Outputs from system to the
surroundings.
boundary
system
surroundings“Stuff” can be a physical quantity (p. ej., masa, energía) or something more abstract (p. ej, information, a signal, or a reading)
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Levels of modeling
An automotive airbag system
A block diagram
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Levels of modeling
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Levels of modeling
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Levels of modeling
This is the “MEMS” you would buy.
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Levels of modeling
This is the “MEMS” you would buy.
MEMSsensor
This is the “MEMS” we usually model.
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Levels of modeling
MEMSsensor
This is the “MEMS” we usually model.
• How many inputs/outputs are there?
• What are the inputs? • What are the outputs?
• What is the relationship between the inputs and the outputs?
• What do we need to know about what is inside the “black box” in order to find those relationships?
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Transducers
Most MEMS are transducers.
Sensors
• Input is some physical quantity whose value we wish to know (p. ej., temperatura)
• Output is some other physical quantity (p. ej., voltage) whose value correlates to the measurand
Sensors measure something
Actuators
• Input is usually a voltage or some other electrical signal
• Output is physical motion of some kind
Actuators move something
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Sensor or actuator?
Thermometer
Input
Output
Thermocouple
Input
Output
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Sensor or actuator?
Bimetallic micro-valve
Input
Output
(http://www.konicaminolta.com)
Ink jet print head
Input
Output
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Sensor or actuator?
Digital micromirror device
Input
Output
Capacitive accelerometer
Input
Output
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Sensor or actuator?
Comb drive
Input
Output
“Micro-reactor” microfluidic device
Input
Output
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Loading
The act of measuring alters the thing we’re trying to measure
loading
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Power input to transducers
Many sensors require a voltage supply as a second input to provide power for signal conditioning—circuits that help convert the output signal to a form useful for the application
Sensors and actuators require different amounts of input power. Sensors are low input-power devices; actuators are high-input-power
devices
Power input Converted into the actuation outputControl input Tells the system what to do
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Transducer characteristics
Static response characteristicsSpan (or full scale input)Range of input values over which a transducer produces output values with acceptable accuracy
UnitsSame as input. (p. ej., Pa for a pressure sensor)
Full-scale output (FSO)Range of output values corresponding tothe span.
UnitsSame as output (p. ej., V for a pressure sensor)
For an actuator? μm
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Transducer characteristics
Static response characteristicsSensitivity Constant of proportionality between output and input for a linear transducer.
Slope of the best-fit line.
UnitsOutput units/input units.
Accuracy How close the transducer output is to
• (sensor) true value of the measurand, or• (actuator) the desired output effect.
Accuracy is determined by a calibration procedure
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Transducer characteristics
Static response characteristics
Resolution
• (sensor) smallest detectable change in the measurand
Unitsunits of the measurand
• (actuator)smallest change in output that can effected by changing the input
Unitsunits of the output effect(e.g., μm for displacement)
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Te toca a ti
For the PX26-001DV model differential pressure transducer:
1. What is the measurand?2. What is the span?3. What is the full-scale output?4. Determine the system sensitivity. 5. Can this transducer be used to measure ΔP, for P1 = 25 psi and P2 = 24.5 psi?
Explain your answer.
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Dynamic versus static response
MEMSTransducer
Steady input Steady output
Time varying input
Time varying output
Static response
Dynamic response
Step input Sinusoidal input
Time
Time
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Response to step input
MEMSTransducer
Response timeTime required for output to reach new steady state value
OvershootAmount the initial response exceeds the desired value
TimeTime
or
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Response to sinusoidal input
MEMSTransducer
Time Time
y(t)
Amplitude ratio (or gain)Ratio of the output amplitude to the input amplitude• Usually reported in decibels (dB)• dB = 20log(gain). Can change as a function of the input frequency
Can be magnified at some frequencies and attenuated (reduced) at others.
FrequencyAmplitudePhase
Same as frequency larger, smaller, or the same In or out phase
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Response to sinusoidal input
Resonance Large magnification at certain frequencies and not others
Phase shift• Amount of by which an output
sine wave is “misaligned” with the input
• Usually reported as phase angle φ = ωt
resonance frequenciesin phase out of phase
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Response to sinusoidal input
(not time)
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Bode plot
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Volunatarios para temas
1. Resistive sensing Piezoresistive sensing Magnetoresistive sensing Thermo-resistive sensing ______________________
2. Capacitive sensing Piezoelectric sensing ______________________
3. Resonant sensing Variable-frequency resonator Variable-amplitude resonator ______________________
4. Thermoelectric sensing Thermo-electric cooling ______________________
5. Magnetic sensing
Reluctance sensing Inductive sensing ______________________
6. Capacitive actuation Piezoelectric actuation ______________________
7. Thermo-mechanical actuation Bimetallic actuation Thermopneumatic actuation Shape memory alloy actuation Hot arm actuation ______________________
8. Magnetic actuation Magnetostrictive actuation ______________________